Microstructural Characterisations of Welded Shape Memory Alloys

Today, with the development of technology, different welding methods are applied for different alloys. In this work, changing of functional properties after using welding methods for NiTi alloy samples was targeted. However, two different welding methods were employed for the same alloy and results were compared to each other and commented on them. In the present study, samples were welded with TIG and Laser welding and their cross section was examined in the joint area. Then these samples were examined in optical microscope and SEM. The advantages and disadvantages of both welding methods were reported. The basic distinction of TIG and laser welded samples examined in microscope was the scale of HAZ area of TIG welded piece. Nevertheless, due to more thermal input is applied for materials in TIG welded parts, more molten materials are detected or heat effects are attained in this practice. In laser welding, heat input is less and this can be recognized from the observed micrographs. While HAZ area is obviously distinguished and welding border zone is detached from the base metal. The twin structures were not observed in optical microscope; for that reason they were investigated in SEM to see these twins in laser welded area.